Acid solution



Patented June 4, 1940 UNITED STATES PATENT OFFICE ACID SOLUTION Netherlands No Drawing. Application July 23, 1938, Serial 6 (flaims.

This invention relates to the art of pickling metals and more especially to means for improving the results obtained with acid pickling baths and for preventing the attack of metals by solutions of acid reaction.

It is well known that metals and metal alloys are attacked by organic and inorganic acids in the presence of water and especially by aqueous solutions of acids. In the pickling of metals with aqueous solutions of acids or acid salts, in order to remove scale and impurities on the surface of the treate me a s, not only the scale and impurities are removed; a certain amount of the metal also dissolves under the formation of metal-salts in the bath, involving a loss of active acid.

One object of the invention is to prevent or minimize the dissolution of metal during pickling and the loss of active acid.

Another object of the invention is to prevent the attack of metals by acidic solutions in chemical and physical processes wherein such acidic solutions are used in metallic receptacles.

Another object is to prevent or minimize the contamination of the air with acid particles originating from the bath and carried into the atmosphere by the hydrogen generated during the pickling treatment, the presence of acid particles in the atmosphere being noxious for the workmen.

Still another object in view is to prevent or minimize the occurrence of gas enclosures in the treated metallic object, such enclosures of gas occurring frequently after pickling processes and being probably due t5 the solution of hydrogen gas developed "by the process in the metallic surface.

A further object of the invention is to prevent or minimize the brittleness of the treated metal which is usually caused by pickling treatment, caused by the hydrogen in statu nascendi developed in the treatment.

Various compositions may be used for the purposes aforesaid, as will be described hereinafter.

According to the invention a non-oxidizing acid solution is used with an addition of an inhibitor of the group constituted by the alkyl-thiocyanates and the aralkylthiocyanates.

The addition of a small amount of these thiocyanates exerts a beneficial action on the pickling treatment and the above mentioned advantages are obtained when using an acid bath to which such compound is added.

In the Netherlands July 28, 1937 Organic non-oxidizing acids, such as formic,

aceticand oxalic acid may be successfully used. are rule it will however be preferable to use a non-oxidizing mineral acid such as lphuric and hydrochloric acid as the acid compound for the purpose in view, though other mineral or organic acids than those above mentioned and aqueous solutions of acid salts, such as sggiium bis ulfa te may be profitably used. Inhibitors, which appeared to be useful according to this invention are e. g. methylthiocyanate, benzylthi dithiocyano-ethane (NCS-C Hz-SCN), and other alkylor aralkylthiocyanates.

In certain cases the protecting action of the thiocyanate contained in the pickling baths can be improved by the addition of capillary active agents, such as wetting agents, and/or foaming agents and/or a er 1 1 o e composion. ponine has been found to be a useful addition.

The addition of an inhibitor other than a thiocyanate, for instance thiocarbanilide, appears to improve the inhibiting action of the thiocyanate and also the inhibiting action of the additional inhibitor.

The thiocyanates have been found to also improve the properties of protective coatings serving to prevent corrosion of metals.

As an illustration of the invention some examples are given hereunder, wherein the results of tests with small pieces of hoop-iron are given.

The examples serve to elucidate and clarify the invention; the invention is however not restricted to the compositions and compounding substances mentioned therein.

The dimensions of the iron pieces were about 4.0 to 2.5 to 0.1 cm., their weight averaged 5-6 grams. The pieces were immersed in the solutions and under the conditions mentioned in the examples.

In all examples 100 ccms. of a 20% acid were used.

Example I Acid HaBO4 HzSOa.

Additi n 0.033 gr. benzylthiocyanate.

Temperature 8P0 80 0. Reaction time... 90min.. 90min. Decreaseolweight 29.3%.... 0.07%. Impedingactmn 99.9%.

Example 1! Example IX cid-. no! n01. Acid 1101...... 110i. Addition. 0.100gr.herylthiocy- .040 gr. benzylthioanate. cyanate. Tem erature 30C 39C 0.010 gr. benzyisul- Beac on time.. Addm 1L nde. Decrease oiweight 0.050 gr. Quimbin (a 1mpedingaction.. not made by V. Servo oi Delden, Holland) Emm le 11] Temperature 40C 40C.

tion time Because of weight... Acid no HCL Impedmg 50mm 0.100 gr. benzylthio- Addition cyanate.

0.400gr.saponine. Example X Temperature 39C 39C. geaction timelgfii ilzgfllin 90min.

359% Acid. H;S04 HQSO HQBO. Impedina 993% Addition 0.025 gr. benzyl- 0.025;. Dr.Voge1s Beiz-Zusatz.

Temperature. 78 C.-. 78 0. Example IV Reactiontima 90min. 90min. 90min Decree a: 0i 56.Zl%.- 0.11% 27.7%

were Acid mach.-. mam. p ing ac 99.8% 50.7%. 0.100 gr. methylthioi .Addition cyanate. i 1 Th its d i hib ti 1 3 re 9 Superior resu an superior n i ng m ?3ihtij::::::::::::: $329.31: 3913?: effect obtained by the composition according to Impeding action this invention is illustrated by the comparative tests reproduced in the following table:

Table Acid HC] H01 HCI HG! H01 HCl. Addition 0.100% Rodinc 0.100% Rodine 0.100% Dr. vogei e 0.100% Ferrophil' 0.(K)%benzylthi(y 40. 41. Beiz-Zusatz. IZExtrem-Sparbeizcyanate.

u Temperature 43 C... 43C 43 (2.-.. Reactiontiine 90min. 90min 90min... Decrease of weight in 12.45..-. 3.10 3.02

percent. Impeding action in per- 75.1 75.7

cent.

1 Made by American Chemical Paint Co. Made by "Chemos" A. 0., Aussig, Csechosiovnkin.

Example V Acid E804... E801. Addition.-. 0.100gr. dithiocyanoethane. Temperature 78 C 78Q. Reaction time 90min..-. 90min. oiweight 77.5%--." 0.650%. Impeding action .2%.

Example VI Acid 38,804"... H2804. Addition 0.025 gr. benzylthlocyanate. Temperature 78 C. 78 q. Reaction time..... 90min. 00min. Decreaseoi weight 77.5%.. 0.171%. Impeding action 90.8%.

Example VII Acid mam--- msot' 0.0125 gri benzylthiocyana e. Adam 0.050gr.dithiocyanoethane. Temperature 78C 78 Q. Reactiontime 90min 90mm. Decreeseoiweight 77.6%..." 0.240%. Impeding action 09.7%.

Example VIII 7 Acid H01 H01.

0.070 gr. benzylthiocyanate. Addition 0.131110i gr. thiocarbane. 0.020 gr. saponine. Temperature 45C 45 C. Reactiontime 90min..- 90min. 'DecreaseQIWeighLHL 16.25% 0.00%.

Impedingaction 100.0%.

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof.

I claim:

1. As a new pickling bath, an aqueous solution containing a substance of the group constituted by non-oxidizing acids and non-oxidizing acid salts and a substance of the group constituted by the alkylthiocyanates and the aralkylthiocyanates.

,2. The pickling bath of claim 1, in which the acid belongs to the group constituted by sulphuric and hydrochloric acids.

3. The pickling bath of claim 1. in which the acid belongs to the group constituted by acetic, citric and oxalic acids.

4. The pickling bath of claim 1, in which the thiocyanate belongs to the group constituted by benzylthiocyanate, methylthiocyanate, dithiocyano-ethane.

5. As a pickling bath, an aqueous solution containing a substance of the group constituted by non-oxidizing acids and acid salts, a substance of the group constituted by the aliqrlthiocyanates and the aralkylthiocyanates, with an addition of thiocarbanilide.

6. The process which consists in pickling metal with an aqueous solution containing a substance of the group consisting of non-oxidizing acids and acid salts and a substance of the group consisting of the alkylthiocyanates and the aralkylthiocyanatcs.

PIE'I'ER FREDERIK FELKERS. 

